After some lenses from eBay it was time again to get a lens brand-new from a reputable dealer. So the Sigma 150/2.8 APO macro will arrive shortly fresh from the factory.
So expect the usual report from me.

Here are the main facts from the catalog:
Size: 80x137mm = nice size 21mm longer than the Nikon 105/2.8 and 7mm shorter than the Nikon 180/2.8
Weight: 833g w/o caps and collar but including lens-hood = very "bearable" and only a little heavier than the Nikon 105 or 180
Optics: 16 elements in 12 groups = much too much for a fixed focal The 105mm micro-Nikkor is a 14/12 design and the (non-micro) 180mm Nikkor is a 8/6 design
Closest focus distance/max.magnification: 38cm / 1:1 Filter-thread: 72mm = standard No IS = very bad AF: HSM, so does work on D40/x/D60-bodies , manual-focus override by turning the focus ring Covers full frame/FX or smaller = normal Comes with an nice looking lens-bagPrice: around 580€ new = not exactly cheap The front-lens-cap is the new pincer-type like Nikon's the rear-cap is cr*p like ever Distance information is relayed to the camera, so the Nikon body can do all the advanced exposure-related stuff with this lens Aperture ring = no, just like a Nikon G-lens lens-shade included and revertable for transport Tripod-collar can be removed without dismounting the lens , easy to turn camera to portrait-mode Limiter switch: Yes, with two positions: "full" or 52cm to infinity / 38-52cm.
Sealing: No unlike the Nikon 105

Versions:
As to lens-mounts: There are versions for Nikon, Canon, Sigma and four-thirds.

Motivation:
Now why should one get the Sigma 150/2.8 besides the micro-Nikkor 105/2.8 VR and the Nikon 180/2.8?
- It's almost 50% longer than the micor-Nikkor, almost as long as the 180mm Nikkor. So a nice length for all those hard to reach subjects
- It's at least as sharp as both of the other lenses
- It can go 1:1, whereas the 180mm Nikkor can only reach down to 1:6.6 which is definitively not enough macro for my liking
- It has the same large f/2.8 aperture
- It has much less Bokeh-CA than the 180mm-Nikkor
- It has a faster focus than the 180mm-Nikkor
So I will surely sell the 180mm-Nikkor if the Sigma holds up on IQ-promises!

Alternatives:
- The micro-Nikkor AF-S 200/4.0: An excellent lens but longer (19.3cm) and heavier (1.2kg) and not as fast. It's also quite pricey at around 1300€ new - The Nikon 180/2.8: A smallish fixed focal with excellent IQ were it not for the surprising degree of Bokeh-CA - The micro Nikkor AF-S VR 105/2.8: again a very good choice including VRII. But in many cases simply not long enough (esp. if you think of a FX-body) - The Tamron or Sigma 180/3.5 macro: nice but not overwhelming - The Nikon 135/2.0 DC: excellent sharpness plus Defocus Control plus f/2.0 aperture. But only 1:7.1 magnification and 50% more expensive

Whoa, the lens arrived this morning at 10!
That's after ordering the lens yesterday at 10 and getting a delivery note yesterday at 1630. And the shop is in Austria So I could already unpack the gear and do some prelim test-shots.
I have also updated the previous post with all the new observations: Yeah, finally a decent front-cap from Sigma. But what is this: no aperture ring? So I have to control the aperture by the dials at the body, just like any "G"-lens from Nikon.
Finish and feel is EX-style, just the focus ring doesn't match the impression: You can definitely "feel" some gear behind the focus-ring unlike the smooth movement of the Sigma 100-300 EX.
The tripod-collar is the same design like with the discontinued Sigma 300 or 400mm. So I can leave one collar mounted to my tripod and just change all Sigma lenses (with collar) within 15 seconds

The max aperture is reduced considerably when focusing close: down to f/5.6! But that's ok as your dof at 1:1 is so razor-thin that f/2.8 is almost a no-no for shooting at these magnifications. At 1:5 (=0.9m distance) the max aperture is f/3.3.

Focusing is fast (enough for me). It's 3 seconds from closest to infinity and back. Focus action is almost 270° and just 90° for 60cm to infinity, which can be travelled in 0.5 seconds. It's virtually silent - very good!
The focus-acquisition is positive even under lower light conditions, hunting can occur but seems moderate at best. I have to retest my micro-Nikkor, but I have the feeling that focus on the Sigma is better than on the Nikkor.

Sharpness wide open seems good center and border. More on that when I've whipped out my Siemens-stars and trained the lens on my trusty Manfrotto perfectly perpendicular to the test-charts...

Colors seem clear, the whites don't show a tendency for "blooming" or "haloing"

The lens might have a slight degree of front-focus and a little field curvature or a minimal decentering defect. But this will show up in the lab-tests. Nothing to worry so far!

And no: This lens doesn't AF with the Kenko-TC It's the same prob as with the Sigma 100-300mm: The HSM seems "too fast" with the TC so the control-loop keeps oscillating around optimal focus. But if you MF (as many people do with their macro shots), everything is fine!

What I'm planning to do next:
- Repeat the Siemens-star test-shots so that they are comparable with my latests reviews. (Done)
- Make same with the micro-Nikko 105/2.8 to stage a real shoot-out between the two contenders (Done)
- Add test-shots with micro-Nikkor 105/2.8 + Kenko 1.5x TC (Done, including Nikon 180/2.8!)
- Find out about the "shrink-factor" when both lenses focus close. I suspect that the focal length of the Sigma shrinks more than with the micro-Nikkor, but perhaps my math is not up to scratch. (Done)
(makes mental note to test the aperture reduction with the micro-Nikkor too) (Done)
- And then there is the dreaded shake-test: the non-OS/VR/IS Sigma in close-up situations vs the micro-Nikkor with VR - both handheld. As this is a LOT of work don't expect me to do this very soon.
- Get a better feeling for focus-performance of both lenses. This is also not easy to achieve.

So in the end you should not only know how good the Sigma is but can also compare it's performance against the "standard" micro-Nikkor.

Well, yes, I'll admit: I haven't done a proper review neither of the micro-Nikkor 105mm f/2.8 VR nor of the Nikon 180mm f/2.8D So I promise to make good on it and do some of the tests for the new Sigma 150mm f/2.8 in parallel on the other two lenses.

So here they are side-by-side:
From left to right: Nikon 105/2.8 VR, Sigma 150/2.8, Nikon 180/2.8

Are these lenses really comparable? Well the Nikon 105/2.8 and the Nikon 180/2.8 not really because the difference in focal lenght is >70% and one is a macro and the other is not.
But if you put the Sigma in the middle like on the picture you have closer matches:
- all are f/2.8
- two are macro
- the 180mm is only 20% longer than the 150mm
- the 105mm is only 30% shorter than the 150mm
- size and weight are very similar
- IQ on all three is very good
- all three are IF (internal focus) designs
- the 150mm + 180mm are non-stabilized
- all are FX-capable
So it would be very hard for me to decide when to take which lens. The only things that are clear:
- for low-light handheld work take the 105mmVR
- for macro work don't take the 180mm

Now let's see how the focal lengths of these IF-designs shrink when focussing close.
From the length of the lens you could already conclude that the 150mm probably shrinks faster than the 105mm. As the 180mm is also quite short relative to it's focal length that might also shrink pretty fast. But at a max magnification of 1:6.6 that might not be a real issue.

Now let's go to the test-parcour at 1:6.6, 1:3 and 1:1. I'll measure the distance from the sensor to the subject (a ruler) to get images 23.6x6.6= 156mm, 23.6x3=70mm, and 24mm wide. The 158mm lens in the tables below is the Nikon 105/2.8 + 1.5x Kenko TC!

The following table shows the sensor-subject distance that is needed with each lens to achieve the afore-mentioned magnifications:
-> with 105mm/150mm/158mm/180mm lens
1:6.6: @88cm...114cm...130cm..150cm distance
1:3.0: @50cm.....63cm.....70cm distance
1:1.0: @31cm.....38cm.....40cm distance

Now, if I put these figures into my calculator for non-IF lenses I can calculate the equivalent focal length at each magnification. These focal lengths will be shorter than the nominal 105/150/180mm that the lenses only achieve at magnifications below 1:50! So let's see which lens has the highest "shrink-factor".

This means that the Sigma shrinks pretty fast: even at only 1:6.6 magnification it already shrunk 13%, which increases to 37% shrinkage at 1:1. The other lenses/combos shrink only about 4-6% at 1:6.6 magnification. The micro-Nikkor shrinks 10% at 1:3 and 26% at 1:1. When used in conjunction with the 1.5x Kenko TC the shrinkage is 17% at 1:3 and also 37% at 1:1, just like the Sigma.

To put the shrinkage into perspective: at 1:3 the front-lens to subject distance with the micro-Nikkor is 50-16=34cm. With the Sigma this distance increases to 63-18=45cm. So it's a gain of a little over 10cm. Whether this helps to capture shy animals may well be questioned.

If you really, really need a good distance from your subject, get the Sigma 400/5.6 APO macro which can go down to 1:3 with a front-lens to subject distance of 1.3m!

Now here's to the next topic: Aperture shrink.
What is it? With most lenses when focusing close the effective aperture shrinks. With the complexities of IF-designs it is almost impossible to predict but at least the Sigma 105/2.8 and the Nikon 105/2.8 transfer the effective aperture to the body where you can see the result from focusing close.
Here are the results:
Sigma 150mm: f/2.8 at infinity, f/3.3 at 1:5, f/4 at 1:2.5, f/5.6 at 1:1
Nikon 105mm: f/2.8 at infinity, f/3.3 at 1:3, f/4 at 1:1.4, f/4.8 at 1:1
So again, the Sigma shrinks faster than the Nikkor.

Phew, I'm through with the Siemens-star test-shots.
3 lenses + 1 combo with a TC at 4 different distances for same magnification, each at around 6 apertures. Controlling the perfectly perpendicular setup plus focus accuracy. Now I only have to make 2 virtual copies (one for center-crop, one for corner-crop) of each of the 24 shots and crop to the relevant segment.
------3 hours later------
Now everything is labelled appropriately and uploaded to flickr...
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How will I present the results? Well, as this is a lens-shootout you will find in each row 4 consecutive crops in 150/105/180/158mm sequence. First row is always the 100% center-crops, the second row is the 100% corner-crops. Starting off on top is f/11 and going down to f/2.8 (except for the Nikon 105+TC which goes only to f/4.0). So here we go:

Observations on sharpness:
1. The results of the Nikon 180/2.8 at f/5.6 are worse than the results at f/4.0, This is clearly an indicator that something was not optimal at that shot: either focus or shake. So I have to repeat it. But the other results for this lens seem to be good (for testing purposes).
2. The micro-Nikkor + 1.5x Kenko TC cannot hold up with the others. Even at f/11 this combo is not better than the Nikon 180/2.8 at f/4.0. Last place!
3. The Nikon 180mm f/2.8D clearly deserves third place! From f/8.0 on (f/11...) it's almost indistinguishable from both macros.
4. Second place is a close call and you have to look very careful for differences between the Sigma 150 and the Nikkor 105. But in the end the micro-Nikkor AF-S 105mm f/2.8 VR came in second place.
5. So the winner is the Sigma 150mm f/2.8 EX APO macro HSM.

This is a fantastic result for this lens! You can easily use it wide-open every time and get the sharpest results were it not for the razor-thin dof if you do macro with f/2.8. But for non-macro shots just pull it (the aperture) open and happily snap away But keep in mind that the price of the Sigma at 570€ vs the micro-Nikkor at 750€ (all prices from reputable dealers in Germany/Austria, incl. 19% you-know-VAT) is not necessarily cheap and the Nikkor has the added benefit of VR image stabilization (no test from me yet) plus weather sealing. So the close second place of the micro-Nikkor is a testament to the excellent IQ of that lens.

Btw.: all test-shots were from a tripod and VR on the micro-Nikkor was off!

You might ask: At which magnification were those test-charts shot?
Well, this was shot from a distance of 3.8m (for the Sigma 150/2.8 ) which gives a magnification of around 1:25.
Yes, you're right: this is not exactly a true macro-test! But with the resolution of the test-chart and such a sharp lens at 1:10 the lens starts out-resolving the test-chart So no macro resolution tests from me today or in the near future

Oh, and by the way: Make sure no sunlight hits the front lens. Otherwise you will be immediately punished with flare! So: always use the sun-shade

Addendum: An added bonus is that the Sigma lens-bag is a perfect fit for the Nikon 14-24mm f/2.8 (a huge wide-angle zoom reviewed here). Thus you can cover 10.7x focal range (14-150mm) plus 1:1 macro at constant f/2.8 aperture with just two lenses: one on your camera-body and one in the small pouch Well, perhaps just put the Nikon 50mm f/1.x in your pocket too